text:
What are the regulations on flying UAVs over people on the ground?
We are considering a project related to drones and in my discussions with people I heard that flying UAVs overhead people (crowds or otherwise) is banned. I also heard this is the case for the USA and EU. I searched and couldn't find the related detailed explanations anywhere.
I would be grateful if somebody could shed some light and point me in the right direction.

Useful site: http://knowbeforeyoufly.org/for-recreational-users/

The general rule of thumb is "don't do anything hazardous for people or property on the ground".
In the US, do not intentionally fly over unprotected persons or moving vehicles, and remain at least 25 feet away from individuals and vulnerable property.
Based on whether your project is for recreation or not, how heavy the drone is,... you may not be able to do the same things. The FAA website has a page titled ``What Can You Do With Your Unmanned Aircraft?'' that gives details on what you can and can't do based on these parameters.
A document published by EASA states that for low-risk drone operations:

Flights above crowds are prohibited, but flights above people not related to the operation in cities or populated areas is allowed.

Refer also to local laws. A number of states and municipalities have passed or are considering limitations on unmanned aircraft.


text:
Can helicopters create contrails?
Can some or all helicopters have contrails? If only some, why only those? If not, why can they not? Pictures would be really helpful. I do know that turboprops and piston props can leave contrails, but I haven't been able to find anything about contrails on helicopters.

They don't typically fly high enough for contrails.

Typical helicopters don't, but the SA315 Lama has flown up to 40,814 ft.

Yes, as a world-record attempt, in general it does not fly anywhere near that.

You don't have to be high to leave contrails. I once saw a Cessna 150 with a short contrail while doing circuits at 1600' ASL on a cold -38C day.

Contrails behind Russian airliner at takeoff:   https://i.sstatic.net/AyLnu.gif

It all depends on how you define the term "contrail".  Conventionally they are considered to be the condensation of water vapor from jet exhaust at high altitudes.  However, I have seen people argue that condensation of atmospheric moisture even at sea level from wingtip vortices is considered a contrail.

@MikeSowsun I wonder if that Russian airport has a trail of deeper snow off the departure end of the runway. - haha

@MichaelHall Given that "contrail" is just short for "condensation trail"; it seems fair to me that the second definition is accurate.  That seems to be how Wikipedia treats it as well.  Nothing about the term "contrail" makes it clear that it has to be from exhaust.  If anything, that's just a bias because of how much more we observe those contrails compared to vortex induced contrails.

@JMac, except "trail" suggests something that persists after the thing that created it has passed out of sight.  But, if you will agree that when I go outside on a crisp winter day I am exhaling "contrails", then I will accept your definition!  ;)

@MichaelHall What persistence has to do with jet engines? WW2 bombers used to make contrails over much of Western Europe by their propellers. The persistence is caused by the atmospheric conditions. https://www.google.com/search?q=ww2+bomber+contrails

@Vladimir F, good point.  And I would agree those are contrails, we just aren't used to prop aircraft flying high enough to create them these days.  What I do not consider contrails are the temporary vapor trials that dissipate rapidly 10-20 feet aft of the aircraft.  But that's just my personal definition...

Once in a great while one can observe a contrail that appears to be sheeting off the entire trailing edge of the wing of a high-flying airliner. It usually happens near cirrostratus clouds-- rarely or never in a completely clear blue sky. Such contrails usually persist for many minutes. I strongly suspect that such a contrail would continue to form even if the engines were switched off. Whether it would be as long-lived without the moisture from the engines mixing into it, is another matter. It would be very interesting to find out.

If the temperature and conditions are right, yes.
Any aircraft which has a heat engine that burns hydrocarbon fuel, which is pretty much any reciprocating or gas turbine engine used in aviation, will emit carbon dioxide and water vapor as byproducts of combustion.  It’s just a byproduct of the chemical reaction to produce heat energy in the engine. And when the temperatures and humidity in the ambient air are low enough and high enough respectively, the water vapor in the exhaust stream will freeze into ice crystals that remain suspended in the atmosphere for a sustained period of time.
You typically won’t see this at your average airport or from the average helicopter flying over you as the temperatures simply are not low enough at the altitude the aircraft operates at for contrails to properly form. That being said, see picture below.

Image source: https://koreaaero.tistory.com/40 (in Korean)

Carlo, that picture  appears to be vortices trailing from the rotor tips.  (and the aircraft is flying above translational lift)

@KorvinStarmast I'm not sure how you can state that conclusively. Contrails don't visibly connect directly to the engines (for example: https://upload.wikimedia.org/wikipedia/commons/4/47/Contrail.fourengined.arp.jpg) and the movement of the rotors may mean they don't point directly back to the engines as a result.

@ceejayoz I use my eyes

Wooooow low altitude rotating chemtrail dispenser ! Sweet !

I very much doubt that those 'contrails' have anything to do with engine exhaust. As I asserted in my answer, the engine exhaust is hugely diluted and dispersed by the downwash and cannot possible leave a trail. The trails seen above are almost certainly from atmospheric moisture.

@Fiddlesticks Contrails from fixed wing aircraft are ‘hugely diluted by wingtip vortices as well.  A helo will produce vortices, rotor wash or no, if the conditions are right.

@CarloFelicione Fixed wing aircraft typically don't have extreme downwash directly through the exhaust stream, though. Especially not aircraft with wing-mounted engines. The wingtip vortices are normally well outboard of the engine exhaust streams.

@reirab actually there is an intermixing of engine exhaust with wingtip vortices which has limited effect on the dissipating of contrails https://cdn.aviationpros.com/files/cygnus/image/CAVC/2013/SEP/640x360/boeing-747-contrails-9740f605-_11174150.jpg

@CarloFelicione No doubt, but it's not extreme downwash directly through the exhaust stream like on most helicopters.

Not just hydrocarbon fuels, burning hydrogen fuel would also create a contrail, wouldn't it?

@KorvinStarmast The rotor will create vortices and since the turbine exhaust ports are (on most models) close to the rotor itself (because that's just where the engines are) the exhaust will be mixed with the air pushed down by the rotor. Thus the hot, humid exhaust will mix with the rotor vortices. Once the temperature gets low enough for the trails to form, they will be mostly indistinguishable from the airflow created by the rotor itself.

@gerrit yes it would.

@reirab, when the helicopter is in forward flight, it will only produce downwash comparable to a fixed wing airplane of similar size and speed.

Once in a great while one can observe a contrail that appears to be sheeting off the entire trailing edge of the wing of a high-flying airliner.  It usually happens near cirrostratus clouds-- rarely or never in a completely clear blue sky. Such contrails usually persist for many minutes.  I strongly suspect that such a contrail would continue to form even if the engines were switched off.  Whether it would be as long-lived without the moisture from the engines mixing into it, is another matter.  It would be very interesting to find out.

Contrails off the engine exhausts is unlikely. But in the right conditions, ie damp air, you can get contrails off the "wingtip" vortices, ie off the rotor blade tips.

Rotor vertices are not contrails i.e. condensed water vapor from engine exhaust

@CarloFelicione I think you're over-constraining the definition of "contrails" when you shouldn't be.  "Contrail" is just short for condensation trail.  Although they are typically produced by the water vapour from engine exhaust, it's not critical to their definition AFAIK.  At least Wikipedia doesn't seem to think so, the article spends quite a bit of time talking about contrails due to changes in air pressure; which is what the contrails due to wingtip vortices would produce.

@JMac  "contrails" was originally a contraction of those two words, but now has a clearly understood definition related to exhaust - that is why the phrase "wing tip votex" exists seperately.

@MikeBrockington The phrase "wing tip vortex" exists separately.  A wing tip vortex isn't the same thing as a contrail or a condensation trail.  A wing tip vortex can trigger a condensation trail because of the low pressure zone; but a wing tip vortex and the condensation it leaves behind are two different things.

In a word: NO.
All existing helicopters have their engine exhausts somewhere beneath the main rotor, and that means that the exhaust gases are hugely diluted and dispersed by the enormous downwash from the main rotor. It simply is not possible for a contrail to form under such dilution and turbulence.

And yet: https://www.metabunk.org/data/MetaMirrorCache/69ba2dca69ac8a46d70f85d2a2158391.jpg and https://bloximages.newyork1.vip.townnews.com/newsminer.com/content/tncms/assets/v3/editorial/7/9d/79d88bd4-7008-11e2-aca8-001a4bcf6878/5111c603aa5c1.image.jpg (found at https://www.reddit.com/r/hoggit/comments/2rty2j/i_spent_30_minutes_to_get_the_huey_to_263k_only/)

@ceejayoz your comment do answer the question and thus should be an answer, not a comment.

@ManuH These images aren't mine, and are thus not mine to share under the StackExchange license, so my understanding is that I can't make an answer that includes them inline.

@ceejayoz why do you believe that is a contrail like the ones from a high flying jet?  See RAC's answer.

@KorvinStarmast Note in the first photo what appears to be denser condensation at the bottom of the trail, in line of the engines. The first photo also debunks the idea that the rotor downwash wipes out any visible condensation put forward in this answer.

I think that this answer would be better if the first line is: "generally, no"  But that's my opinion.

@ceejayoz 1) Comments are licensed under the same terms as any other content that you share. 2) Linking to the original source is all that's required of you to be compliant to the license. You can't claim them as your original content.

@GalacticCowboy Links to copyrighted material don't violate copyright law. Copying it over to Imgur does. Links have a tendency to die; on StackOverflow a links-only answer gets removed. I'm not familiar enough with the rules here to know if the same is true here.

@ymb1 Read that answer again. "That means that the images you upload are covered under our 'attribution required' license just like anything else you contribute." I cannot license someone else's photos under that Creative Commons license.

@ymb1 Just because imgur won't make a claim of copyright on it doesn't mean that you can legally upload it there if someone else owns the copyright and hasn't given you permission to post it there.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

authors: Vladimir F Героям слава

sort: votes


text:
Where can I get test samples for Assistant Air Traffic Controller Officer exam?
A few days ago, I applied for the position of Assistant Air Traffic Controller Officer (AATCO), for CAA in Pakistan. The next step is a written test.
What am I supposed to prepare specifically?
My background is in software engineering. Any help/reference will be appreciated.

I assume the CAA themselves should tell you. Their ATC requirements are here and my best guess is that the written test will be for English proficiency (see section 6.3). But I know literally nothing apart from Google can find and I have no idea about specific questions.

any portions..?

Based on the country you are looking for the certification, rules may be slightly changed. For India following syllabus is applicable (Source: atcguild.com)
At present it is a year-long ab-initio training (Under revision to make it in two sections of six months each)
Modules:

Air Traffic Services
Aerodromes and Ground Aids
Air Legislation
Meteorology
Communication Procedures
Technical
Search and Rescue
Air Navigation

The selection shall be made on the basis of a

Written test
50% questions on subjects relating to educational qualifications
prescribed
50% on General Knowledge, General Intelligence, General Aptitude,
English etc. Voice test
Personal Interview
Medical fitness as per ICAO Annex-1

I Googled for the subject, but didn't find much information on the paper patterns or example papers.

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text:
Can the parking brake be set on an 737-800 if the aircraft has no power?
If a 737-800 has no power ('dead' airplane), is it still possible to set the parking brake on? If so, how?

Good question, here is a guess: in contrast to a car where you can pull the handbrake up (and you pull it quite a long way), the parking brake on a plane is usually set using a small leaver. Since with that you probably won't be able to get the amount of force needed to secure the plane, there must be something else. This could by a hydraulic valve that is opened when the parking brake is set, but then it'd probably need power to be released (though it be smarter doing it the other way around). I don't think it is anything like it, and I guess setting the parking brake requires power.

This function is provided by the parking brake valve which is an electrically-operated hydraulic valve that, when the parking brake is commanded to be set, closes and traps hydraulic pressure in the brake lines. You set the parking brake by pushing both brake pedals all the way down, and then pulling up on a separate lever that locks the pedals in the applied position and at the same time commands the parking brake valve to close and trap the hydraulic fluid. You can then take your feet off the brake pedals.
If there's no electrical power, that valve can't close. If there's electrical power, but no hydraulic power from the pumps, that valve can close, and the hydraulic pressure to hold the brakes is then supplied by the accumulator. But that's not as reliable as having the hydraulic pumps operating, and you're not assured that the pressure supplied by the accumulator is sufficient to prevent airplane movement.
Moreover, closing the parking brake valve doesn't ensure a perfectly sealed system. Over time, internal leakage will mean that, if hydraulic power isn't constantly supplied, the trapped brake pressure will gradually leak to the point that the brakes can't hold the airplane, even though the parking brake lever and the brake pedals in the flight deck are still locked.

Nice answer, do you have any sources for this by chance?

One minor addition is that the accumulator will start at system pressure, but will slowly bleed down over time. If the airplane is going to sit for a long time; chocks should be used on both sides.

U can use parking brake with accumlator fully charged but u must have the accumlator fully charged with 3000 psi , that fully charged accumlator will keep the parking brake applied only for 8 hours only depending in the internal hyd leak.

What about electrical power? (see the other answer)

U just need the batteries on to supply a signal to close the parking brake solenoid valve .

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

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text:
Is TCAS II required in the US?
I would like to know if, in addition to any MEL requirements, there is any regulation or requirement about having an operational TCAS II while operating in US airspace?

If EEUU means the US, it's better to use the English abbreviation than the Spanish one.

TCAS II is required for most airline flights. This is not a requirement for certification, and the TCAS may or may not be on the MEL. However, most flights under part 121 (scheduled airline service, as well as some freight) require TCAS II.
As noted in FAR 121.356, "Turbine-powered airplane of more than 33,000 pounds maximum certificated takeoff weight" must be operated with equipment that meets a list of standards, but is essentially equivalent to just requiring TCAS II. Smaller aircraft with 10-30 seats can use TCAS-I.

No.  It's not required in the United States.  There is nothing in Part 25 of the regulations.  However, if you install one it should comply with this AC.
www.faa.gov/documentLibrary/media/Advisory_Circular/20-151B.pdf

Part 25 covers the design of the aircraft, Part 121 covers the operation. There are many things not required in a Part 25 aircraft but required to operate it under Part 121 and similar. Systems like TCAS are some examples.


text:
Why do full service airlines prefer to run a separate low-cost carrier?
There are various full service carriers (FSCs) who have a separate low-cost carrier (LCC) subsidiary. For example:

Germanwings by Lufthansa
Air India Express by Air India
JetKonnect by Jet Airways

Why do the FSCs prefer to launch a separate LCC, rather than providing seats at a cheaper rate with reduced comforts within their existing structure?

It may be of interest that not only airlines use this tactic. Companies like Unliever or Procter&Gamble try hard for their brands (ranging from washing powder to Pringles) not to be percieved as connected to one another or to the parent company.

@PavelPetrman: Also brands can be sold by Unilever to P&G, or Sara Lee, and vice-versa.

They still want to get into the low cost segment but want to market themselves differently for better penetration. You can only present so many images of a brand to customers: You can't show both the super-cheap prices with happy youth on them and posh first class at the same time.
They do not want to tarnish a nice brand by mixing it with a low cost carrier and what that is perceived to entail. For instance, Germanwings got a somewhat infamous reputation recently, and Lufthansa is probably happy their name was not more frequently used in media. Low cost is also associated with less good customer service and hidden fees.
Crew are often less well paid, and they are sometimes put under a separate working agreement and company to try to prevent conflicts. Some legacy carriers have very good pay which is difficult to reduce. Management does not want to be bound by these when expanding or adjusting their business.

Each case is pretty specific depending on exactly they are trying to do and achieve. For many American Carriers and Lufthansa, the last one is probably the principle reason.

"For instance, Germanwings got a somewhat infamous reputation recently, and Lufthansa is probably happy their name was not more frequently used in media." - if you are referring to flight 4U9525, as far as I remember, about every single news article that I happened to read about the incident said something like "Lufthansa subsidiary GermanWings". In fact, the tragedy was how I first learned that GermanWings has any connection to Lufthansa at all.

@O.R.Mapper indeed, but it's still more abstract than the main brand itself. It's generally now pretty consistently referred to by the Germanwings name. Take Colgan Air Flight 3407 that was actually Continental Connection flight for instance.

Despite having read reports of the incident, I learned just now (as far as I can recall) that Germanwings was a subsidiary of Lufthansa. If I did not have a particular interest in aviation I still would not know this, so apparently the parent company can avoid some unwanted "name recognition."

As mentioned there are lots of branding issues around this but there are also lots of corporate and legal reasons to do so.

Business Isolation: If you want to start out a bunch of new routes and you are not sure how well they are going to do a large airline my not want to book that kind of loss or risk having to cover it. Thus they can incorporate a "new" airline and protect their existing and profitable business interests should the "new" airline go under. Likewise it also makes it easier, should it be very profitable, to potentially sell it off (or absorb it as well).
Taxes/Fees: Tax law changes from place to place so this may differ depending on where they are based but if there are different taxes as a result of company size or specific aviation taxes they may be able to take advantage of them by splitting up.
Legal Isolation: I am no lawyer but I am sure that how ever they set these up it isolates the parent airline should anything happen to the other carrier.
Image/Branding: this has been touched on already but as mentioned you may not want the image that comes with running a low cost brand associated with your luxury brand.

I would imagine this has to do with branding.  Kind of like how some car companies have both "regular" and "premium" brands.  Eg., Chevy v. Cadillac or VW v. Audi, etc etc.  It allows for companies to have a more exclusive version of their product for people who are just the premium, exclusive sorts...
Granted there are other cost considerations, and other branding considerations, and I could probably sit here and go on for hours with that but I think it would be a little bit outside of scope.
So, to just give a basic explanation:  Different brands have different associations with them.  Some are seen as premium, exclusive, indulgent.  Others are seen as just hitting the basics.  And some companies will avoid mixing the two just for the sake of brand identity in marketing.

As mentioned in earlier answers, branding and management (pay, collective bargaining agreements, etc.) are certainly two major factors. And legacy airlines are mindful of the risk to see their profit cannibalised by the new cheap fares so they need to maintain as much segmentation/price discrimination as possible.
Interestingly, the two strategies are not exclusive. Air France/KLM has several low-cost subsidiaries (Transavia, Transavia-France and HOP!) but also introduced many low-costs tactics (no meal, surcharge for hold luggage…) on short-haul European routes on both legacy airlines.
The thing is that some elements of the low-cost model (paid refreshments, quick turnaround, routes to cheap airports or use low-cost terminals at major airports, single-class cabin with as many seats as possible, identical aircrafts…) can only be introduced for the whole airplane or even the whole fleet. And for a highly price-sensitive market segment, merely using some elements of the model to offer lower prices is not enough, you need to go all in to ensure your fares are as low as those of your direct competitors (say Easyjet, not necessarily Ryanair).

This is the idea (rather than the brand segmentation for marketing purpose). But probably the compelling reason is to have a different cost structure, starting with radically different policies: wages and advantages for the employees (not only the crews), suppliers and contractors T&Cs, premises, management staff, etc. In short they run a different company with no constraint related to the main brand. Ther new company may even make comparable or better profits, but in case of losses, then the main brand profits won't be hurt.

Actually they have 2 low cost: Hop ! and Transavia

@Antzi I added that to the answer, thanks!

A business reason no-one has mentioned yet is the original reason the big names started:
Because low cost airlines began flying routes cheaply and created a market
If the big names hadn't joined in, all that revenue would have gone to the low cost airlines, who would have grown to the point they could potentially compete in the existing markets, so it was essential that the big players joined in.
It is not possible to run a low cost airline in the structures of a major airline (the cost model is entirely different - passenger demographics, services on board, pre-flight hospitality, additional benefits etc.) so the only way to do it that makes financial sense is to run it as a separate logical entity.
It has proven to be a difficult change for some of those big airlines, with various attempts at creating budget versions failing, but some have managed to compete successfully.


text:
Why aren't contra-rotors used on the V-22 Osprey?
The Osprey has 38 ft (11.6 m) rotors in a rotating nacelle on each wing. The rotors are powered via a gearbox as in usual turbo-pro fashion.
Is any reason that is obvious that smaller contra-rotating rotors wasn't adopted. It is noted on Wikipedia that the rotor diameter is currently 5 ft (1.2 m) below ideal, wouldn't a contra format be more compact on this front.

Due to the requirement for folding rotors, their 38-foot diameter is 5 feet less than optimal for vertical takeoff, resulting in high disk loading.

@jCisco Are you suggesting the use of two sets of contra-rotating rotors instead of two simple rotors? or do you mean one set of two contra-rotating rotors?

the reason for them not being used on multiengine props in general are due to increased costs and reduced availability of service

Contra-rotating rotors over simple rotors @mezzanaccio

@RonBeyer, turning is done by differential tilt. Not having contra-rotating rotors just means there is always some difference compensating that torque.

If you really mean contra-rotating (= each side having two rotors on a common shaft) rather than counter-rotating (= each side turning in different direction, which it does), the reason is obvious: it would be totally absurd. It would have no benefit (due to counter-rotating, there is no net torque already), it would just be significantly more complex.

Also, contra-rotating rotors would not increase the area anyway. Because for contra-rotating rotors, the area only counts once as it's the same air acted on by both rotors.

@JanHudec about the would not increase the area anyway I think that's the point of the question: OP suggests that contra-rotating would DEcrease the area required, while reducing the current high disc loading.

@Federico and my answer is it wouldn't. For efficiency what matters is the area in plan view and if there are two rotors above each other, the area counts just once. So contra-rotating rotors of the same diameter would be considered to have the same loading and would require almost the same power (a little saving is made due to the second rotor stopping the rotation of the air, but that's somewhere on order of 6%).

Is any reason that is obvious that smaller contra-rotating rotors wasn't adopted.

Smaller contra-rotating rotors would not have higher efficiency!
The efficiency of lift/thrust generation by propeller increases with the amount of air it affects. But when you put one rotor above another, they both affect the same air, so efficiency is not increased.
Contra-rotating rotos are only slightly more efficient, compared to single rotor of the same diameter, because the second rotor counters the rotation of the slip-stream behind the first one that otherwise also carries away some energy. But typical saving due to this is around 6%, which is by far not enough to warrant the hugely increased complexity, especially in the most critical component of a rotorcraft, the gearbox.

Picture source
Co-axial rotors are insanely complicated. The V-22 had to overcome many first time problems and is very complicated. Combine the two, and you'll have a bunch of weeping engineers and no product.
On a co-axial rotor:

Both the rotors need to have their individual swash plates being able to generate collective and cyclic inputs. But one swashplate is above the other.
if the rotor heads are fully articulated, there needs to be enough distance between the two to allow for differences in flapping dynamics. But a rotor high above the helicopter creates a bit of a construction problem.
The rotors turn in opposite directions, requiring two different sets of gearing & drive train, all sharing the same axis centre line.

Aerodynamically, co-axial rotors can deliver a higher end thrust than a single rotor of the same diameter, at the expense of less efficiency: the same mass of air is accelerated to a higher velocity. The obviously less complicated solution of a greater diameter rotor, accelerating more air, runs into its limits when the blade tips approach supersonic speeds.
The Osprey tilts its rotors to be able to fly faster than a horizontal rotor helicopter, the limiting factor again being blade tip speed, but now in the propeller way. The Tu-95 does use contra-rotating propellers, to be able to fly faster than with single propellers with the same thrust.
Picture source
So yes, aerodynamically two sets of co-axial rotors would have benefits for the Osprey. But it would be an impossible engineering challenge, the Osprey is pretty complex and had plenty challenges to solve as is. Have two sets of co-axial rotors and tilt them? No way.

Aircraft design is always the art of finding the right compromise.
Even if a feature might promise to increase efficiency in some way, this may come at a great price.
If your suggestion were to be implemented, the aircraft would go from having two rotors (which is already a high number) to four. I am not familiar with the specific design, however these are in my opinion some of the drawbacks that would arise:

Increased complexity: increases the effort of design, operation and maintenance.
Rotor systems represent a significant portion of the overall aircraft production costs, hence this solution would surely bring about a significant increase in unit cost. Also consider you would have at least 8 blades to maintain instead of 6.
Increased structural mass.
Possibly increased noise emission (though I am not so sure about this point).

Most aircraft designs would surely have more unconventional features if the only thing that mattered were increased performance or efficiency. However other aspects are often just as important, if not more.

Based on the picture in ymb1's answer, you would have 6 blades per wing instead of 3, but your point still stands.  :)

@FreeMan there you see how unfamiliar I am with the Osprey! Thanks for pointing it out


text:
Does temperature affect dynamic pressure?
Taking off on a cold day (5°C), it can take 10 seconds to reach rotation speed but on a hot day (40°C) degrees it will take longer to reach the same speed.
Is this due to the dynamic pressure? How does temperature affect it?

Huh? Dynamic what?

Are you asking about how temperature affects ram air pressure and static air pressure (and as a result indicated airspeed) or are you asking about how engine performance changes due to temperature?

how temperature affects ram air pressure and static air pressure.

Yes, temperature affects dynamic pressure by affecting air density: it reduces with increasing temperature.
Dynamic pressure q $ = ½ \cdot \rho \cdot V^2 $
The molar form of the ideal gas law: pressure p = $\rho \cdot R \cdot T$, with R = gas constant and T in degree K
$$\rho = \frac{p}{R \cdot T} \tag{1}$$
Eliminate $\rho$ from dynamic pressure:
$$q = \frac{p}{2R \cdot T} \cdot V^2 \tag{2}$$
From (2) we can see that if temperature increases, dynamic pressure decreases linearly. In a deleted answer @xxavier mentions correctly that Indicated Air Speed is a measure of dynamic pressure, so let’s compare the two situations. 5°C = 292K, 40°C = 327K, TO true airspeed on a cold day = $V_c$, on a hot day = $V_h$
$$ \frac{p}{2R \cdot 292} \cdot V_c^2 = \frac{p}{2R \cdot 327} \cdot V_h^2$$
$$ V_h^2 = \frac{327}{292} \cdot V_c^2 => V_h = \sqrt{\frac{327}{292}} \cdot V_c  $$
$$ V_h = 1.058 V_c \tag{3}$$
So to reach the same IAS, TAS must be 6% higher. But there are more ways that dynamic pressure affects time to reach rotation IAS:

The propeller thrust is proportional to air density: simple momentum theory models thrust as $T = C_T \cdot ½ \rho A \cdot (\Omega R)^2$. Again density $\rho$ which decreases linearly with temperature according to (1). Propeller thrust reduces with factor (292/327), integrated over time until $V_h$ is reached. 11% less thrust to reach a 6% higher velocity.
The engine has less dense air to operate with. From this site:

When your engine is not equipped with a turbo- or supercharger it will also suffer from the less dense air. Each intake stroke (which is by volume) will contain less air molecules and thus less power can be developed by the engine (due to the fixed fuel / air ratio).

So yes, dynamic pressure plays a role, but the real underlying cause is the less dense air everywhere. Also in the dynamic pressure.
Notes:

All above comparisons at equal static pressure $p$.
$V_c$ and $V_h$ are actual true airspeeds, not indicated speeds.

I suggest a change, instead of inserting the values right away and then solving for vh just use the variable names and solve that equation. Then you get a formula v_hot = v_cold * sqrt( T_hot / T_cold ) and you can any values that you like, and it doesn't just the values given in the example

A nitpick, "11% less thrust to reach a 6% higher velocity".  1.06 squared is around 1.12.  This is the increase in drag going 6% faster.  But it isn't doing that either (IAS).  The Density Altitude (PV=nRT) is actual molecules per cubic foot that the prop bites and the plane moves through.  True airspeed will be higher "high and hot", and with less thrust, it will take longer to get to IAS needed.  Up to the point where not enough thrust is produced (too high and/or hot).

@Jan Yes I know, that is how we are taught at school. I chose not to do that here, for readability purpose.

@RobertDiGiovanni 232/327 = 0.893

@RobertDiGiovanni Please read the answer again. It does not feature a state of the art pressure container. It does state that IAS needs to be reached in order to fly, and that TAS is 1.058 higher in the hot day case. And there is 11% less available thrust to reach the same IAS (higher TAS), with an equation to prove it. For the form of ideal gas law that contains density, please scroll down in this link, the fourth equation under Molar Form.

11% less available thrust, got it.  Good answer, thanks.

Dynamic pressure q = $\frac{1}{2}\rho \cdot u^2$, with $\rho$ is density, u is flow speed. It is a measure of aerodynamic pressure at a given speed and is expressed in pascals or psi.
This value is the origin of the term "Max Q", which is the maximum aerodynamic stress a rocket experiences when launched and is accelerating through the atmosphere.
Since it has a density term, it is part of your answer, but the solution is not usually described with the term Dynamic Pressure, it is described as Density Altitude.
Density Altitude is Pressure altitude corrected for temperature.
So you get your pressure altitude by setting your altimeter to 29.92 and reading the altitude.
Then Density Altitude is calculated as P + (120x(OAT-standard temperature))
Standard temperature is 15 Celsius at sea level, BUT it decreases 2 C with every 1000 feet of altitude.
So now pressure and temperature on a 40 C day make you "high and hot".
What this does is give your prop less air to "bite" at max rpm, resulting in less thrust.
With less thrust, your plane will take longer to reach its rotation speed due to slower acceleration ( a = f/m ), and because it will have to accelerate to a higher speed to get enough IAS to lift off.

As with the conveyer belt question, ground speed at takeoff (wheel rotation) will be higher, so good tires and well greased bearings are in order.

Have added some MathJax, you can roll back the edit if you don’t like it.

Sure, when it's hot the indicated airspeed is lower than normal for a given true airspeed, due to reduced air density, and air density is indeed a factor in dynamic pressure.  The relationship between air temperature and indicated airspeed is same as the relationship between air temperature and dynamic pressure, and both are due to the relationship between air temperature and air density.
Of course, power and thrust are also less on a hot day.  That has to do with air density too, but not in a way that directly involves dynamic pressure.

"where is this temperature"(ground, air, water, space), what is the medium(dirt vs asphalt vs rock vs mountain vs altitude vs clouds vs sun vs rain vs tides vs waves vs saltwater vs freshwater etc etc" and by "dynamic" what is the driving force?(propeller, impeller, turbo jet, ram jet, lifting body, wing loaded lofting body, rocket, hydrofoil, etc etc). Yes of course higher temperature equals greater pressure in a vacuum but there are "inversions" in physical reality where in fact pressure will drop as temperature increases and vice versa. Since a presume by "dynamic pressure" the question pertains to an object with a given forward velocity of some specified medium many right answers would suffice provided there is actual experience and pertinent physical data observed, collected, houses, studied etc none of which is presented here.
"Start with an instrument that can measure pressure" by way of example and go from there.

I don't think you know what dynamic pressure means...


text:
What does the NCrit parameter indicate in a CFD analysis?
When analyzing an airfoil in the XFLR5 software I am asked to input some data regarding the free stream. For this, a dialogue box pops up that has the following options:

One field contains the expected Reynolds and Mach numbers for the flow.
The other field says Ncrit. What is this parameter, and what does it have to do with the trip location (top and bottom) which can be inputted together with it?

I'm voting to close this question as off-topic because it asks about features of a particular software package, rather than about aviation, per se.

I believe the question has some merit since the feature it asks about is not exclusive to this software, but rather an established part of the larger field of computational fluid dynamics.

You should make basic research (such as wikipedia) and indicate what is your current level of understanding so that answer can be as precised as possible and adapted to your current knowledge.

The whole setting group is called transition settings, and refers to the boundary layer transition point (from laminar to turbulent).
The forced transition trip locations are exactly that, expressed as a fraction of the chord, for the top and bottom surfaces. They are akin to placing a trip strip at those locations.
The Ncrit value is a measure of free flow turbulence and is used to simulate the transition location when no forced trip location is given. XFLR5 uses the same method as XFOIL, which is an adaptation of the $e^N$ transition theory. Note this linear theory loses its validity at a fluctuation level of 1 to 1.5 percent, which corresponds to an N-factor of 6.9 to 7.3, meaning it is not suitable for highly turbulent flows.

As to what this is important for, the turbulent or laminar nature of the boundary layer affects flow separation and viscous drag. A turbulent layer will generate more drag, but separate at higher airfoil angles of attack.
Where this gets really interesting is at low Reynolds numbers, where a laminar layer will detach, but become reattached if turbulence is introduced into the airflow ahead of the airfoil, such as by a turbulator. It will then remain attached if the turbulator is removed, displaying a hysteresis loop. The same effect will of course occur in the opposite direction, with a barely attached turbulent layer detaching and staying that way if the free flow turbulence decreases enough to cause it to turn laminar.
I must note that this effect is confined to low Reynolds numbers, on the order of $10^4$.

The NCRIT is the same as in XFOIL.

@PeterKämpf thanks, I was looking into that. It seems XFOIL uses a simplified version of the e^N theory, though understanding how exactly it differs would take me a while.

Thanks a ton @AEhere !!


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Would adding a slat and a slotted flap increase the max CL of a multi element airfoil to 6.5?
Would adding a slat and a slotted flap increase the  of a multi element foil to 6.5?
I understand, as a general rule, the max $C_L$ for a classic NACA airfoil is as follows:

Base: 1.5
Slat: + 0.7
Slotted flap: + 1.3
Total $C_L$: 3.5

But with a Selig multi-element foil, the starting max $C_L$ is around 4.5.
Would adding a slat and flap to a Selig airfoil, with a 20° deflection of the main foil, increase the  $C_{L_{max}}$ to anything close to 6.5? Assume a Reynolds number in the 600-900k range.
Here is a pic of the foil:

An examination of soaring (eagle/vulture) bird wing tips may yield a design potential, especially if a lot of excess power is available. Draggy, yes, but lift they will.

The theoretical maximum lift of a cylinder is 4π. At that point the forward and rear stagnation points coalesce on the bottom of the cylinder. Practical solutions use rotating cylinders (Flettner rotor) but will not reach this theoretical limit.
This should illustrate that 6.5 is not outright impossible but the distance between a cylinder and an airfoil is quite large, so this theoretical limit does not apply to airfoils.
Adding a slat and a slotted flap to a regular airfoil will bring you at most to a c$_{l_{max}}$ of 2.8. Now you want to add them to a multi-element foil. Would that be several slats and flaps in sequence? Practical solutions use a single slat and a multi-slotted flap where the deflection angle of the single flap elements increases along the flow path of the air. A typical example would be the airfoil of the Boeing 727 which had a triple slotted flap which could reach a two-dimensional c$_{l_{max}}$ of 4.2 with 60° deflection and rearward movement of the flaps which increased the effective wing area. Note that wing sweep and ailerons reduced the practical maximum lift coefficient of the full aircraft to 3.0 (see plot below, taken from A. M. O. Smith's excellent article High-Lift Aerodynamics).

With modern CFD this could be improved a bit, but then the preference of aircraft builders has been to reduce the number of flap elements while losing only a little of lift.
Another practical limit is the maximum Mach number in the suction peak of all the airfoil elements. Once this reaches 1.58, no lift growth could be observed in experiments. This translates to a maximum for the product of Mach squared and pressure coefficient of -1.0. In other words: You need to fly very slowly in order to achieve high values of c$_{l_{max}}$.
The only practical design I know which reached that magic limit of 6.5 given as the c$_{l_{max}}$ of its wing airfoil is the Antonov An-70. Here this number is valid for the inner wing which is immersed in the prop wash of the mighty Aerosila SV-27 propellers, driven by the 13,240 hp Progress D-27 turboprop engines. By using the flight speed and clean wing chord for the reference parameters, this looks to me a bit like cheating. But the achieved lift is real!
EDIT:

Now that you show the Selig airfoil, it should be obvious that it is a point design for maximum lift and no practical applicability in real aircraft. Neither will it allow a thick spar nor low drag at lower lift coefficients. Adding a slat will help little, because the limiting part is the pressure rise on the main airfoil. The accelerating flow up to a chord of about 20% is meant to increase the area in the c$_p$-plot and the pressure rise aft of this point is a Stratford distribution which maximizes pressure gain without separation. Reduce pressure in the suction peak only a bit and the flow will separate, and lift collapses.

A cylinder is the shape of theoretically highest lift? Goodness, that's a surprise. I'm guessing its drag is astronomical too, given planes don't have cylindrical wings?

@Dannie a rotating cylinder. See: https://en.wikipedia.org/wiki/Magnus_effect If you are interested in what a cylinder has to do with airfoils, look up the Zhukovski transformation.

@Peter Kampf re max cl of 2.8.  As you can see, a multi element foil can have a much higher cL max than a single element foil.  I'm sure a slatted and slotted multi element foil could be modelled in java foil, if one had the time...

@Dannie: This is only valid in the theoretical realm of irrotational and friction-less flow. In the real world it can be approximated by a Flettner rotor but practical airfoils do not make use of that effect.

In my account, it suggests offering a bounty for this question. What is a bounty?

@Fred: May I refer you to the help pages?

@ Peter What if the airfoil was something like a Selling1233, which is used for aircraft?  it starts with a max cL of about 2.5, so adding a slat and flap, could theoretically bump up the cL to about 4.5, no?

@Fred: The Selig 1223 is still a point design with high camber and low thickness, but missing the slotted flap. Yes, adding a flap and slat will increase lift coefficient, but not to 4.5 – note how much more camber and lower thickness is required on the Selig multi-element airfoil to achieve those 4.5.

@Fred Now I am curious which real-world design (not model aircraft!) used the Selig 1223. It is not listed even on Michael Selig's own page to airfoil usage.

@Peter: Thanks for all your insight. I never studied aerospace engineering, so all of this is like drinking from a fire hydrant. I'm just a ultralight pilot trying to design and build the ultralight of my dreams. lol

As far as I no, the Selig1233 is only used on model aircraft for now, but I understand  there is some talk of using it for a cargo plane.  I'm contemplating using it for my STOL biplane ultralight, but not 100% convinced.  I imported it into XFLR5 and I've got a model that has good stability analysis but I think it's too hard to get the cg just right. I might revert back to a NACA2415.  Why do you say it's a point design? It seems to work pretty good in Xfoil from -15 all the way to +40 AOA!!

Aerofoil.net shows it dying at 15deg AOA, but that's not what xfoil spits out. It drops a bit at about 15 deg AOA, then flattens out to 40 deg AOA. Super thin though, so to avoid a ridiculously heavy spar, I think it lends itself to  a short span biplane/triplane ultralight with struts, maybe a box wing instead of using end plates, in my humble opinion. lol

@Fred: Seriously - You trust XFOIL at 40° AoA? Please - this is no wind tunnel, but a simulation based on potential flow plus some boundary layer magic. It cannot hope to come even close to what happens in separated flow. Yes, the Selig suits itself to a biplane, but then you repeat the mistake of all the early pioneers. Thick airfoils work better. If all you want is STOL and a small speed range, the Selig is a good pick.


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Why use turbofan engines for high altitude flight?
I noticed that a lot of high altitude aircraft have turbofans for engines. So I researched and figured out that turboprop engines are more efficient. But most high altitude aircraft like the Global Hawk and U-2 have turbofan engines, with some exceptions like crazy long-endurance solar-powered aircrafts.
Is this because the low density is a problem for turboprops? or why?

Possible duplicate of Why do jet engines get better fuel efficiency at high altitudes?


text:
What do airliner manufacturers do with aircraft for which have no buyers?
"White-tail airliners" refers to either airliners without any customer order (like the beginning of A300 production), or those where the order was cancelled after/during production and where no new purchaser has been found (like the Skymark A380 deal).
How do the manufacturers handle the white-tail airliners?

Sometimes ostentatiously

Maybe they get thrown in the discount bin with a 60% off sticker on them?

@abelenky buy 3, get one for free...

New airliners without a buyer will be handled on a case-by-case basis. Of course manufacturers prefer to not be in such a situation, and there is no standard system for handling this. However, there are some typical ways that this is handled.
One option it to store the aircraft at the manufacturing site. This is the same (and pretty much only) option that is used for aircraft without engines. This has the advantage of being easier to work in and deliver, but will of course take up valuable space.
To save space at the factory, the aircraft can be moved somewhere else. Storage areas already exist primarily for older aircraft being stored or scrapped, but new aircraft can go there as well. Boeing has done this with some 747-8 aircraft, as well as C-17's.
Of course the manufacturer has spent money assembling the aircraft, and it is costing money to have it sit somewhere, so they will be eager to cut their loss as much as possible. These aircraft will probably be offered at a significant discount compared to placing a new order. However, buyers may prefer to wait and receive an aircraft straight from the factory, rather than one that has been sitting in storage for a while. There may also be issues with customized options applied for an original buyer that would need to be refurbished or accepted by a new buyer. Looking for new buyers and rearranging deliveries is not unheard of and is part of the business of making aircraft.
It may be that no one is willing to buy an aircraft, or the aircraft would otherwise not be economical to put in service. The aircraft may in this case be sent to a museum, as with the RJX. In a similar case, the first three 787 aircraft were not deemed economical to put into commercial service after the test program, and were sent to museums.
The last resort would be to scrap the aircraft. This is certainly disappointing for a new aircraft, but in some cases it is the only option left to regain any value.

Don't potential buyers have to pay at least a part in advance? How is that handled in such cases?

Yes, buyers generally pay some amount when placing an order. Which cases are you asking about?

Of what range are we talking here? Like 20% of the final price? 50% or like 5%? I'm just wondering what happens to this money. I think that the manufacturer keeps it anyway.

@PatricHartmann they have to pay part in advance, which is typically non-refundable like it is with any purchase (it's pretty much a guaranteed amount the supplier will get even if the customer goes out of business). Worse, they may be held liable for even more cost due to breach of contract (depending on the wording of the contract of course).


text:
Will IATA codes run out?
Three letter combinations gives $26^3=17576$ possible codes. Some airports have multiple codes (ARN = STO, for example).
I’m just going to guess that there are more than 17576 airports in the world. Are we reusing these codes?

Actually, in the case with ARN and STO, STO is not specifically for Arlanda, but for "all" airports in the Stockholm metropolitan area (BMA).

In short, the people sitting over the nose wheel use the ICAO codes, and the people in the back use the IATA codes.
The IATA is the International Airline Transport Association. The ICAO is the  International Civil Aviation Organization. While you are correct, the IATA does not have more than 17500 codes, their primary concern isn't creating codes for every airport including grass strips and private airfields. It is easy to think of IATA codes as being concerned essentially with identifiers that the passengers will need.
As far as ICAO is concerned, they contain a country identifier in their codes. They can even be more than 4 digits, as in the case of RU-2244 (Ukrainka Air Base). The vast majority are 4 digit or 5 digit, with the first 1 or 2 as the country code.
This allows ICAO to be available for every airport in the world. It is very common to refer to the IATA codes when flying locally, let's say within the USA, and refer to the ICAO if flying internationally.
I have a database structure of all airports in the world (or at least all known ones). This includes any grass/water/helipad/paved runways.
There are a total of: 46,465 airport/airfields including those that have been closed.
Source: http://ourairports.com/data/

Hm, I wanted to say that I recently noticed at least two airports that were missing from ourairports (and recently means a couple of months ago), but they were both added since.

As a side note, many airports in the U.S. do not have ICAO codes (or IATA codes,) but only FAA identifiers. Scheduled passenger service airports normally have all three, busier GA aerodromes normally have ICAO and FAA, GA aerodromes with less traffic normally only get FAA.

As of June 2015, fewer than 2500 IATA codes have been assigned. Codes can be reassigned over time. According to the Wikipedia article on IATA codes there have been several IATA codes that have been reassigned. IATA has a mechanism for assigning these airport codes that's available online. Although your original calculation came to some 17000 possible codes, there's a wide variety of reserved codes, and prefixes, so it's actually less than 17500.

Actually, it's MORE than the 17000 calculation, even with reserved, as numbers are allowed too.

@BrianKnoblauch In IATA codes? Are you sure? I know they're used in ICAO and FAA codes, but I've never seen a number in an IATA code. The wiki for IATA codes seems to suggest that they're letters only, but, of course, wiki isn't always right.

@BrianKnoblauch Unfortunately, according to IATA documentation, I can't share the numbering restrictions, but at least on first reading, it appears to be a subset of A-Z.

@SargunDhillon, can you link to the IATA documentation or at least add the section identifiers so others can look them up independently?

@FreeMan https://www.iata.org/publications/pages/coding.aspx - it's $545

@SargunDhillon - nevermind... :(


text:
How can I calculate the cabin pressure following a decompression?
What are the calculations to determine the level of cabin pressure at a given altitude once the cabin is punctured?
I was unable to determine the window size and the flow rate of the compression system on the recent Southwest accident aircraft, for example.

Cabins are typically pressurized to approx. 8,000 feet of pressure-altitude.  That is 75kPa, or 22 in Hg. Why do you want specific calculations?

I've edited the question to show that I want to find the cabin pressure with the window out.  Does it reach equilibrium or does it maintain a higher pressure. In order for that question to be answered, someone will need to calculate it, they may as well share their work.

It stabilizes at external pressure, in 40sec or less.
Air pressure at 30kft = 4.37psi, cabin pressure at 8kft = 10.92psi, from a calculator the flow rate through a 12in orifice at this differential = 475cuft/sec, volume of 737-700 cabin = 9000cuft, time to expel cabin volume holding all this constant = 19sec. Double this time for a linearly decreasing pressure differential.
Commercial aircraft exchange their cabin air 10-15 times per hour, or once in 4-6min, so the pressurization system will not be able to come anywhere close to keeping up. Without descent the cabin reaches external pressure in about 40sec. With descent it is even faster as the differential is lower, and therefore reached sooner.
There was a question about the source of the calculator flowrate. I looked at three:
http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm#calc
http://www.pipeflowcalculations.net/orifice.xhtml
https://www.engineeringtoolbox.com/orifice-nozzle-venturi-d_590.html

It would be good to provide references, especially for how you calculated the flow rates.

Flow rates are available from any of several calculators that deal with piping of gases. You have to find one that can deal with the structure sizes and pressures involved. At best I would consider this a rough approximation, but I think that is all that was needed.

Thanks for the references they were just what i was looking for.

You should read through this paper it outlines a lot of great info on calculating valve size for cabin outflow valves in pressurized aircraft it also addresses your second point (to an extent) on the flow rate of compression systems. The issue you will encounter is that the calculations will only hold for a controlled situation i.e. a situation where you have precise control over the valve (hole) size and can account for small leaks.
In the most generic terms you can find the calculation for flow rate through a hole in a pressure vessel here.
Your specific example is going to be a bit more complex since after a cabin pressure failure the plane will begin a descent rapidly to 10,000ft. so your exterior pressure will be rising as your interior pressure drops (you will need to factor that in to make the above solution a complete result). You also need to consider the airflow over the airframe its self since you are talking about a situation where the aircraft is in flight you have some fluid mechanics to play in as well.
Its called explosive decompression for a reason, its going to happen very very fast.

Also, trying not to be grim, but a passenger apparently plugged the hole temporarily until other passengers could pull her back in. Unfortunately she did not survive it. I'm sure it would have been quite violent.

@TomMcW there was a similar situation worth reading up on here Im sure both incidents were horrific to live through.

@Dave National Airlines 27 was a very similar situation.

The forces involved are astonishing. Air velocity at initial decompression would be nearly sonic, and the pressure if the window sealed rapidly and completely would be around 700lb. She died of blunt force trauma.

@Dave: At least the British Airways pilot did live through it.


text:
Why has the European Union banned several airlines?
The European Union does not permit the entry of several airlines in any of its member states. It does so to ensure the safety of its own airfields, as it feels that management of several airlines is not caring enough. How is this justified?
No such ban is implemented by any Middle-East or American country, which have a very good safety record. What are the EU's views on banning airlines?

one argument could be Charkhi-Dadri mid air collision, but India allows all Kazakh Airlines anyways..

You can't really judge airline's safety from accident. One occurence might be just a bad luck.

you answer your title question by yourself: It does so to ensure safety of its own airfields. The real question, "How is this justified?", I feel that is not about aviation.

A better question would be why allowing unsafe airlines would be justified. In general, the U.S. and Europe have very good airline safety records and they want to keep it that way. For example, none of the major U.S. airlines have had a passenger fatality from a crash since 2001 and there have been only 3 or 4 such incidents on the U.S. regional airlines in that time (and none since 2009.) There has only been one crash resulting in a passenger fatality on a foreign airline in the U.S. since that time (Asiana 214.)

"How is this justified?": Assuming you mean what are the legal reasons given. Inspection on EU airports have shown anomalies in aircraft security, crew qualification, or in the way aircrafts / airlines are inspected by national agencies. The applicable regulation is 2011/2005. | More.

Read this question yesterday and today read this http://www.bbc.co.uk/news/world-asia-33951854

EU ban is not only aimed at European airspace safety but also at passenger safety. It is forbidden for Europeans company to sell plane tickets from banned airlines

@mins not so in a lot of cases. The majority of the airlines on the ban list have never operated services in or into the EU.

@jwenting: Reasons for banning are explained for each airline in the list itself. Either they don't comply with the ICAO Foreign Operator Check criteria (self assessment), they are indeed not authorized to fly in EU airspace, or anomalies where found "during ramp inspection under SAFA program".

@mins i was commenting on the claim that they were banned in order to keep the EU skies safe. Which isn't the case for a lot of them.

I think the policy is completely justified. An analogy: You wouldn't allow an unsafe and unapproved car onto a highway in Europe where it presents a unjust danger to everybody else.
You have to remember that the European Union is a fairly compact bunch of nations: To get to Paris from Southeast Asia or Africa, you're probably looking at overflying at least two or three other countries. Thus, a single flight will have wider implications and involve multiple nations. The policy keeps everybody somewhat happy that they have safe airlines in their airspace. It also keeps their own citizens off the airline in question.
I do not think that it is a question of 'caring'. If they do not feel that the airline can safely fly, they ban it. Note that a fair number of the EU blacklist are automatically banned by country if they have insufficient oversight. It's also not a permanent 'thing' or sentence. Garuda Indonesia was on the EASA blacklist for two years until they brushed up, and are now back flying into the EU. Perhaps it might even have been good, since it pushed the company to improve their standards?
Here is a recent quote on the Iraqi Airlines ban:

ATW understands from unidentified sources that 600 non-EU airlines had applied for TCO authorization. Most had been granted with few problems, but a small number of airlines were subject to greater scrutiny because of their perceived high-risk status. Source

While perhaps less prominent, I think the United States will quickly block any unsafe airline from coming in, although perhaps on a more case-by-case basis. I believe there are other hurdles, such as airport security requirements, that have to be settled to fly into the United States and can act as barriers. I believe the same applies for any other nation.
Other countries say no as well, just perhaps not being as 'vocal':

Some Thai-registered airlines earlier faced flight restrictions by Japan, South Korea and Indonesia, following an audit of Thailand's air operations by the UN-based International Civil Aviation Organisation. In June the agency raised a red flag over aviation safety standards and gave the country until November to tackle the issue. Meanwhile, the US Federal Aviation Administration (FAA) last Friday gave Thailand 65 days to address shortcomings it had found. Source

The project existed earlier but there is a clear and immediate reason for the creation of the first EU “black list”, it's the West Caribbean Airways Flight 708. The crash created a lot of emotion in France. Here is a Guardian article from the time.
After that crash, the EU felt the need to be seen as “doing something”, especially since many passengers might not even have realized they booked a ticket on flight operated by some unknown third-country carrier. You can debate the wisdom of the approach or many other details of the current rules but the timeline is clear.
But the EU did not invent the concept, other countries (and also EU members states) did and do ban airlines from operating on their territories. And the justification is indeed that these airlines have serious deficiencies in their fleet, management and procedures. Even if you are personally not convinced, why would you expect that any other justification would be needed?


text:
How do we determine whether the airfoil trailing edge should be cusped or pointed?
I'm working on a project and I need to decide whether an airfoil has a cusped or pointed trailing edge given the x and y coordinates of the airfoil.
What is the difference between the two trailing edges?

Both cusped and conventional airfoils have pointed trailing edges. The lower trailing surface is concave on cusped airfoils, so plot it and get your straightedge.

In geometry a cusp is formed when two lines converge to the same tangent, or, as Wikipedia puts it:

a point on a curve where a moving point on the curve must start to move backward

For airfoils with an infinitesimally thin trailing edge, the two options are either a point or a cusp:

In real life, an airfoil will have neither, as the trailing edge will have a finite thickness, but for design and analysis purposes, a point or cusp are simpler to work with.
The issues with cusps were well known to early aerodynamicists, as the Zhukovsky transformation produces cusped airfoils, which are impossible to construct in reality, as the converging tangents at the trailing edge also demand infinitesimal thickness.


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How hard would it be to convert a glider into an powered electric aircraft?
How hard would it be to convert a glider into an powered electric aircraft?
I'm thinking something that looks like this:

Would it be as simple as mounting two electric motors and props to the wings and plugging it into power the electronics and a battery system?
Any thoughts?

How hard is it to convert a carriage to a automobile?

i think that might actually be harder because you would have to make a linkage between the engine and wheels. With a glider its a direct motor to air transmission.

I guess ill just have to try and find out ;)

@user3528438 How hard is it to convert a scooter to an electric scooter, or a bike to an electric bike?   Also with gliders there is an intermediate waypoint of the sustaining motor glider, whose engine is too small for self-takeoff.

Re "How hard is it to convert a carriage to a automobile?", Quite easy. People add motors to skateboard, coolers, picnic tables and a lot of weird things all the time. Is that the point you were trying to make?

Just make sure the motor doesn't rip the thing apart. It's not built to be powered after all.

Add-on motors ARE/were common for bicycles and boats, no?

@DanielCaoili: Nothing's stopping you from putting a propeller on the carriage either. "Automobile" does not require the driving force to come from the wheels.

"Hard" is a matter of opinion. But installing an electric motor on a glider is quite doable. You don't want to put motors on the outside, though. Would make more sense to do what most manufacturers do, put the motor on a retractable pylon behind the cockpit, with doors that open and close as needed.

Otherwise known as a motor glider.

Sometimes. It can also be just a sustainer engine.

And you especially don't want to put the propellors on the wings, unless you also install a taller undercarriage :-)

Where I come from these are called gliders fitted with a noise generator.

@jamesqf: above-wing engines are a thing.

It's not obvious to me that an arbitrary glider has the structural strength to tolerate the addition of an engine and, even worse, it's vibrations. Then you have issues with weight and cg. You may want to clarify if you include "flyable" in "doable".

It has been done!
In 2008 an Edgley EA-9 Optimist glider was "converted" in very much this manner for a university project, by strapping eight pylons to the wings, each containing a battery pack and two electric motors - one pushing, one pulling - for a total of 16 motors. This might make it the aircraft with the most engines in history!
It was test flown in this configuration by legendary glider pilot Derek Piggott, then 86, which might make him history's oldest test pilot as well.
Note however that the aircraft was not self-launching - the objective was to see if the electric propulsion system could sustain the glider in flight after an initial aerotow launch.
As a further bit of interesting background, this aircraft is the only example of this type of glider, designed by John Edgley, who is better known for designing the unusual Optica.

Wow, that's even more engines than Helios's 14.

This is awesome. It looks like i might not have to 'reinvent the wheel' if i ever decide to try this. They way the motors are mounted is interesting. I think using smaller-ish (or bigger-ish RC) motors is the way to go since the economy of scale advantage.

How does it not destroy the outboard propellors when landing?

@jamesqf It's a high wing aircraft and the propellers aren't large, it looks like even the outboard ones would have ground clearance on a flat surface. Not so much in the long grass shown, but when landing a glider you keep the wings level until you've come to a complete stop balanced on the mainwheel, before letting one wing gently down. So at worst you'd be lowering a blade into the top of the grass with the prop stopped.

Depending on your definition of "aircraft" (the first stage of a rocket does fly in the lower atmosphere, after all) the first stage of the Soviet N1 rocket sees your 16 puny electric motors and raises you 30 NK-15 rocket motors. Granted, it will also probably explode.

I think the big deal in trying to do this is the mounting. I feel like just mounting onto the outside of the wing is inadequate. What I think needs to be done is have some aluminium pipe directly welded to the internal wing spars and structure. And then have some kind of outside interface that the motors can be bolted onto.

Yes it is very doable and is a project I've been thinking of doing.
The path I would go would be to purchase an amateur built sailplane with good performance like an HP-11 or HP-14.  As an amateur built you can modify it easily paperwork wise.
A glider like an HP-11 that weighs 650lbs and has an L/D of 37 makes 17lbs of drag when flying at max L/D, and you get somewhere around 4-5lbs of thrust from each horsepower with a prop, so the power required to fly level is somewhere around 5 hp.  For decent acceleration and climb performance however, you want several times that, at least 100-150lbs, so you need an electric motor that makes at least 20hp, maybe 25 or 30.  These sorts of motors are readily available nowadays for electric paramotors.
You want simple simple simple, with the minimum performance penalty.  This means NO crazy motor folding gizmos, or exotic mounting.  You simply mount the motor on a fixed pylon adapted to the structure around the wing center section, finely faired, with a trail-folding prop.  With good streamlined fairing for the pylon and motor and the prop folded back, you might lose, at most, 10-15 points off the L/D.  An electric motor glider with a 22 to 27:1 LD is still a pretty good proposition. Not as good as one of the newest high performance electric sailplanes, but you'd only have about 20% of the money into it.
A battery pack would be mounted above and/or below the wing center section in a stainless steel vented fire proof box, with the motor and batteries right on the CG.  Based on the numbers I see for electric paramotor setups, 50lbs of batteries might give you around 30-45 min, enough for a launch and several climbs to altitude, or a fairly extended time cruising level with the motor only running at 10 hp (increased from 5 to make up for the drag of the pylon and the higher all up weight - you'd have to increase the gross or reduce your payload obviously).
The main downside is the downside suffered by just about all motor gliders, higher sink rates. It's like water ballast you can never get rid of, so you won't be able to thermal very well on really weak days, but the ability to self launch and operate independently more than makes up for that.
An alternative would be to mount two smaller 15 hp motors on the leading edge on each side in small faired nacelles, but the installation would be a lot more complicated and you would need to find a feathering propeller, which may be tougher to find than a folding one.

Or you go directly with a PIK-20E or similar and get the crazy motor folding gizmo for free. Batteries go into the wings, where they replace water ballast.

Yes but it's a certified glider and you'd have to do it as an STC/STA and would be extremely costly.  This is a cheapo(-ish) project for a hard core self tinkerer.  Has to be a homebuilt.  A 20-E sells for, what, 40k+ and a conversion you could legally install would cost another 20.  An HP-11k you can get for under 10, and a power installation you develop yourself with off the shelf paramotor based bits another 10.

I don't really like those top rear mounted big propellers. It makes it more dangerous to stand on top the plane/glider in mid flight, lol. but also I think it'd cause too much pitch forward force.

You would have a nose down pitching moment with power, but it doesn't seem to hurt the other retractable engine motor gliders with 40hp 2stokes on pylons.  It's a characteristic you'd have to work around.  On a glider where it hasn't been done before, you would get towed the altitude the normal way to test the flight characteristics the first time.

Was waiting for Peter K to jump in on this one, so I'll recite some of his knowledge.
Notice the sharp nose and leading edges on the OP question photograph compared with the more blunt nose of the glider picture provided by Juan J.
The OP glider is fully optimized for Vbg and may be a little twitchy in pitch under power.
So, certainly you can power it, but to enjoy the wider speed ranges of powered flight (with a wider variety of AOA), you may wish to pick a different glider (you'll have a lot of buyers for that one).  Or, if a little twitchy is OK, go for it, keeping CG and wing load limits in mind.

The blunt nose mainly means it will collect more bugs. The blown T-tail can be arranged to compensate for the engine pitch by giving the elevator some more positive camber. I say more because a regular glider elevator already has some camber for proper stick forces over speed.

Unless you can put the complete propulsion system in the back seat of a two-seat glider, you will have to redesign the whole aircraft to take account of the changed mass distribution.
But if "replacing almost everything" counts as "conversion" then … yes, you could do it.

The proposed system is a battery-electric aircraft.  Balancing one of those is no problem: put the battery and motor on opposite sides of the center of mass.

@Mark So long as you've got some kind of gear linkage from the off-centre motor to the central prop. You don't want the prop off-centre as well, for obvious reasons. :) Motors are generally pretty light though compared to batteries, and a gear linkage is losses you don't need, so probably better to fill both sides with batteries and put the prop directly on the motor assembly.


text:
When are pilots required to have approval to conduct practice approaches?
I would like a clarification about requesting practice approaches.
I have seen pilots at uncontrolled airports shoot practice approaches such as VOR, SDF, etc. without needing approval; obviously.
Am I correct in thinking that a practice approach approval is only required to be explicitly requested when being controlled by ATC via flight following or approach/tower control?
I know this may seem like a silly question, so I will describe a scenario so that readers understand the context of why I am asking a little bit better:
A VFR flight passes through class C airspace, and contacts approach control prior to entering.  On the other side of said class C airspace, a few miles out of the boundary line, there is a destination airport where the pilots would like to shoot a practice approach, which is a non-controlled airport outside of the boundaries of "ATC-contact-required" airspace.  Do the pilots request a practice approach, or do they request to terminate radar service and then go ahead and shoot the approach?
Maybe the answer lies in the content of the approach depending on whether or not initial fixes or a missed approach segment would lead a flight into "ATC-contact-required" airspace.

if you are doing a "silent" practice approach outside of an area where you are required to be in contact with ATC, then you could interfere with another aircraft along the same exact route and altitude as someone who is conducting a practice or real approach under ATC.

@rbp this is true, and you would be well within your rights to do so, and both you and the other pilot would have see-and-avoid responsibility.

Usually airports with approach controls will have it printed on the approach plate. Take for example the non-towered field Menominee-Marinette Twin County:

The approach control frequency is highlighted in the chart. This is who you receive approach clearance from. KMNM is outside of KGRB (Green Bay) airspace by a good 40 miles, but KGRB approach control is responsible for the airport.
So the short answer is: Look at the approach plate for the responsible frequency/agency for the airport.
I think the other part of your question is more along the lines of "If I'm shooting an IFR approach, am I required to get clearance via ATC?" This I'm not 100% sure about but I would guess that the answer is "yes" since you don't want to interfere with traffic shooting real approaches.
The Aeronautical Information Manual has advice for conducting practice approaches in section 4-3-21 (Page 204):

(a) ...Practice
  instrument approaches are considered to be instrument approaches made by either a VFR aircraft not on an IFR flight plan or an aircraft on an IFR flight plan.
  To achieve this and thereby enhance air safety, it is Air Traffic’s policy to provide for separation of such operations at locations where approach control
  facilities are located and, as resources permit, at certain other locations served by ARTCCs or parent approach control facilities.

(Emphasis mine)
Furthermore, it goes on to say...

(b) Before practicing an instrument approach, pilots should inform the approach control facility or the tower of the type of practice approach they desire to make and how they intend to terminate it, ...
  (c) At airports without a tower, pilots wishing to make practice instrument approaches should notify the facility having control jurisdiction of the desired
  approach as indicated on the approach chart.
  (e) VFR aircraft practicing instrument approaches are not automatically authorized to execute the missed approach procedure.

But as I say in my comment, the AIM is a guideline, not a rule and I don't think there is anybody stopping somebody from doing an instrument approach without controller notification, however because ATC isn't providing traffic separation at that point, it could be considered negligent of the pilot to not request ATC clearance. Besides, a good portion of conducting practice approaches is talking to ATC.

So weather aside, during VFR, VMC flight, the determining factor for needing permission to shoot a practice approach is whether or not an approach control is listed on the plate?  Do plates without an approach control even exist?  If having an approach control does mean that you have to get permission for VFR, VMC practice, then I know a lot of people who have been breaking the rules for a long time.
Can anyone find an approach plate without an approach control listed?

Aeronautical Information Manual Section 4-3-21 (page 207) has advice on doing practice approaches. Specifically (c): "At airports without a tower, pilots wishing to make practice instrument approaches should notify the facility having control jurisdiction of the desired approach as indicated on the approach chart." The AIM is not a FAR however, and while probably not breaking any FAR, its not advisable to conduct approaches without ATC. Aside from that, ATC comms are a good portion of a practice approach...

@MortensenAviation it says "approach control facility" -- which could be a TRACON ("approach"), but in more remote areas is an ARTCC ("center")

Great answer!  Thank you. I'm not sure why the answer was down voted.

@MortensenAviation Who knows, some people downvote without commenting meaning I can't address concerns of the quality of the answer.

While the citation from the AIM is accurate, it doesn't reflect at least some real-world situations. In my experience, VFR aircraft don't request practice approaches to a non-towered airport from Approach - we just hash it out on the CTAF. Never heard of anyone being violated for that.

@NathanG I agree, as I say the AIM is a guideline, not a law/rule. I didn't hint at a violation for going against it, I say that its required (by AIM) but as far as I can tell not by FAR's.

THere's always the threat that if you use poor judgment by ignoring something in the AIM, then you could be cited for 91.13 "Careless or reckless operation"

FWIW, I was on VFRFF last night and requested a practice approach to an uncontrolled field, and Center’s response was “you’re VFR, do whatever you want”. That’s a big difference from the TRACON where I usually practice, which requires even VFRs to get an approach clearance.

After reading this thread I opted to call Seattle Approach control and spoke to the operations. They told me, as long as you have a a transponder, have squawked VFR, and as long as you are staying in the vicinity of the airfield (10 miles) they can see you. You don't have to contact them . You are also required to transmit on the CTAF throughout your approach so the VFR traffic is aware of your whereabouts and intentions. It might be different in your area, so I recommend you contact your local approach control indicated on the approach plate to make sure they are ok with you shooting approaches under "VFR" conditions and that you will maintain a look out using a safety pilot.

You are not required to request a practice approach. You are, on the other hand, required to follow the proper technique for flying in whatever airspace in which you happen to find yourself.
For instance:

In Class E or G airspace with an operating control tower, you have to receive clearance to land. In addition, if you have an operating radio, you must receive clearance to approach within 4 miles of the airport below 2500 feet AGL.
In Class A, B, C, or D airspace, you must maintain two-way radio communication with ATC and comply with ATC’s instructions and clearances. If ATC authorizes you to self-vector for a straight in approach, you can maneuver however you wish as long as it’s done safely. Otherwise, you will have to request an approach (practice or not). Also, requesting the practice approach will make ATC’s job of aircraft separation easier and safer. They can anticipate your actions.
In Class E or G airspace without an operating control tower, you do not have to request a practice IAP approach. On the other hand, you will have to request an actual approach if IMC conditions prevail unless you are NORDO. When performing an IAP approach, you will have to make proper radio calls in a manner that a VFR pilot at a pilot-controlled airport would clearly understand. Give your position as a distance and direction heading inbound (presumably) to the airport with an altitude. Make your intentions of an approach and landing clear. Many VFR pilots will not understand the verbiage and nomenclature used for IFR procedures and reporting points.

I don't believe there are any Class E/G towered airports; by definition a towered airport must be Class D or better. Do you have any examples otherwise?

@randomhead, You are assuming that towers have to be permanent. You are also backward-defining Class D airports. Class D airports have to have a tower. A towered airport does not have to be Class D or better. A Class D tower can be full time or par-time operable. When the tower is not in operation, the airspace becomes either Class E or Class G. This will be noted on sectional charts and detailed in US Chart Supplements. True Class E and G airports can have temporary towers for special activity such as air shows. These occurrences will be NOTAMed.The regs for it will be in Part 91.126 & 91.127

Good point about temporary towers. I still believe a temporarily towered airport will become Class D; see for example page 18 of the 2019 Oshkosh NOTAM which mentions "the Oshkosh Class D airspace." Do you have an example of an airport remaining Class E even when a tower is operational?

@randomhead - Thanks for the KOSH info. Although, I am unsure how this pertains to temp towers. KOSH isn’t NOTAMed as temp Class D. It is currently listed as a permanent part-time Class D in the US Chart Supplement, I am not sure if and when it went from being a full-time Class G. But, the temp towers I am talking about don’t have to be permanent physical structures. Just a temp ATC presence. This would not change the fields Class status in the supplement. It would be NOTAMed to inform pilots to treat it like a Class D lite due to the presence of control. I will keep an I out for such a NOTAM.

@randomhead - See the info provided in the following links about temporary control towers.  KJYO Leesburg is an example of an airport with a tower that is not a Class B, C, or D.    https://www.boldmethod.com/learn-to-fly/regulations/temporary-faa-control-towers/ .       https://www.leesburgva.gov/departments/airport/about-leesburg-executive-airport/remote-air-traffic-control-tower

Ah, nice catch. If you look up the NOTAMs for JYO there is one about the tower hours of operation but none saying that there is Class D airspace in effect during those hours. (Of course it is within the DC SFRA/FRZ so two-way radio communication is still a requirement.)

From an answer on another question I came across this document describing a temporary tower operating at a normally-Class-G airport. The document explicitly says that the airport will be Class E with an operating control tower. So there you are, I was wrong!

If the approach (and published miss, if you plan to use it) is entirely within class E/G airspace, there is no regulation requiring you to contact ATC for approval for practice under VFR.
However, please call them anyway. They may be working other aircraft on that approach, either real IFR or other practice VFR, and keeping those folks separated from a non-participating aircraft will greatly increase everyone’s workload and reduce their safety.
Also, a significant part of instrument training and proficiency for most pilots is improving radio skills and working within “the system”, so unless there is a specific reason to avoid it, take every opportunity to improve.


text:
How should private airports or locations not regularly intended for landing be identified if you land at or take off from them?
How are runways on sectional charts that are listed as private identified?
Lets say I fly from a public airport to a private strip; I would log the departure airport as BNA, but what would I list the private strip as?
Generally, what is the accepted norm?

Is this US specific? Or are you interested in general/ICAO conventions?

Where are you logging this?  Pilot log book, booking out at the departure airport, flight plan?

Possible duplicate of How does the FAA determine which format of location identifier to assign to an airport?

@Lady_A I'm not asking how the identification of airports are determined when they're named, I am asking what you log an airport as in a logbook if it has no identifier on a sectional chart and is not included in an AF/D.

@DaveGremlin Pilot logbook.

@Jamiec I am not concerned with whether it is FAA/ICAO.  Answers for one or both are still value-added I think.

In EASA land, for my log book, I just use names.  For example Old Warden to Little Snoring (both are unlicenced private fields).  I record my first visit to an airfield on a separate page and that includes the IACO code if there is one

In the USA, as far as your logbook is concerned, FAR 61.51(b)(1)(iii) only requires "Location where the aircraft departed and arrived," not the 4-letter ICAO identifier of your airports. When you abbreviate the airport with its identifier, that's all you're doing: abbreviating. You could, for instance, write "Nashville International Airport" instead of "KBNA."
Seaplane and helicopter pilots often land in places that aren't even airports. You might log the destination as "Murphy Lake" or "Walmart Parking Lot." Such is the standard convention.
For purposes of the flight plan, there are a few options if flying to a location that has no identifier. On an ICAO flight plan to a location with no identifier, you would enter ZZZZ as your airport, and in the remarks section include a DEST/ group including the lat/long of your destination. For instance, I think DEST/3607N08641W would work. On an FAA flight plan, you can list the nearest waypoint to your destination, and again, describe your actual destination as a common name or lat/long in the remarks.

Those of us with wheels on our planes have also been known to land in places that aren't airports, e.g. dry lake beds.  And FWIW, I don't think I've ever used those 3/4 letter codes in my logbook, if for no other reason than that if I look back in it, I'd like to know what place(s) the logbook entries refer to without having to look up the codes.

@Dave-CFII I think you bring up a great missed point here.  There are tons of "non-airport" destinations for perfectly legal operations which clearly kills any idea that you must log an airport much less an ID.

Ditto to above. It's fun to land on roads.  Log every landing!

I would use the airport identifier, if available, or the name on the sectional.
For example, on this section of NY sectional, you can see several (Pvt) airports, they are indicated by red R in a circle.
PASPORT is enterable in skyvector.com as a destination, as is WATERS.  Entering them as a destination, skyvector will change them to an airport identifier, which you can then type in as a waypoint.
B&B, just north of PASPORT, can't be entered as anything I could find to start.
But, dragging the pink route line, it can be pulled over B&B and then it shows up with an identifier you can use.  Same with the Unknown airport south of 9B1.
If you click on the Departure or Destination airport, skyvector will open more info for that airport, and from there a list of all airports and their identifiers in the state can be selected.  B&B and Unknown are both listed there.

You can also put the name into Airnav and get the identifier that way.

Huh - I would have thought "unknown" would either have tons of matches, or been unrecognized - yet there it is, 1MA5 in Southborough, MA.

Whoever named 1MA5 as "Unknown Field" must have had a weird sense of humor.

One of the pilots from 9B1 created that strip, he was a former airline pilot I believe. Passed away a few years ago.  I think the runway might be a road in a housing development now.

@CrossRoads In southern Florida, on the northern shore of Lake Okeechobee there is Okeechobee CO (OBE) airport, and just to northeast of that there is a private (maybe not) one labeled as "Objectionable", but has no "(Pvt)" label.

Interesting name.  Pvt label appears to be missing, but the 'behind the scenes' info shows Sunniland Ranch is Private use: https://skyvector.com/airport/08FD/Sunniland-Ranch-Airport   There are quite a few private airfields in that area!

@RyanMortensen "Objectionable" is something different and worth its own question.

Ditto to above.  It's fun to land on roads!  Log every landing.  Ditto for those sailplane outlandings.  If you are staying near an airport, you aren't really trying.  It's a fine thing to be objectionable.


text:
What additional US-power or ICAO requirements apply to a departing US-based crew with a US-registered aircraft flying to land in Mexico?
What are additional requirements (equipment, licenses, identification, etc.) for a flight operation with a US-based aircraft and crew leaving the US to enter and land in Mexico that are imposed on the operation by the US authorities such as the government or any of its agencies and comprehensive international agencies such as ICAO?
This differentiates from similar questions because I am not asking about the governing set of laws in international territory or what laws of a different country than the home country would apply to the flight; of course ICAO is international in all cases so could be applied as valid in any home country that an aircraft may depart from.  Each other, non-US, country's specific laws may vary, so they are removed from the scope of my question.

Does this question help? If not, it would help if you can tell us exactly what isn't already covered in it. Also, which part(s) are you asking about: 91, 135, 121...?

@Pondlife all us-government or us agency rules, so not only limited to 14 CFR.  I'm not sure what isn't covered in your other answer.  Maybe everything is?  I actually don't know the answer to my own question, so I can't say with certainty from the negative.  As an example, insurance for Mexico is likely not a rule imposed by a US authority; it's just good, friendly advice. I am attempting to exclude the massively broad scope of every country in the world, that's why I am not asking for Mexico's rules too, and I have only selected Mexico as a generic example which is probably simpler to go to.

Including all possible regulations from any government agency seems very broad and probably mostly off-topic. Are you including things like ITAR, for example? I don't see how this site - or any StackExchange site - could provide a comprehensive answer if your question is really that broad.

No because it is about general international rules. This is the aviation site, so it goes without saying that rules pertaining to ground vehicles or any general travel are beyond the scope. Things like that I would ask on Travel SE.

The only aviation-related requirements on crossing the US border are:

All flights crossing the US's Air Defense Identification Zone (ADIZ) in either direction must be on an IFR or DVFR flight plan, talking to ATC and have a discrete transponder code.
A list of all passengers and crew must be filed with eAPIS at least 24 hours before crossing, in either direction, and the plane must have an eAPIS decal.

The only difference between leaving vs entering that I'm aware of is that you don't need to leave from a designated port of entry. (Some other countries do require that.)
As a practical matter, there are a handful of aviation-related things that apply to most/all other countries that US pilots don't have to worry about in the US:

The pilot(s) must have ICAO-recognized license(s). FAA Student, Sport and Recreational licenses are not.
The pilot(s) must have appropriate medical certificate(s). No BasicMed.
The aircraft must have a normal airworthiness certificate. No experimental aircraft.
The aircraft and at least one pilot must have FCC radio licenses.

Technically, you don't need passports to leave, but you'll need them to go anywhere else (and to return) by air, so they are effectively required for both.
There are thousands of other laws that apply to all people or goods leaving the US regardless of mode, such as not exporting restricted technology or weapons, human trafficking, fleeing prosecution, etc.  (And there are even more for entering.)  I doubt anyone could list them all, and that is probably off-topic anyway.


text:
What is a "Land And Hold Short Of" light?

A runway inspection found a "Land And Hold Short Of" (LAHSO) embedded light had become dislodged and had caused damage to a tyre.

http://avherald.com/h?article=4bb1964c&opt=0
What is such a light, and what does it look like?
See also How are runway lights constructed?


text:
What is the difference between high altitude vs low altitude approach?
Is there any factor that influences the decision of whether to take a high or low instrument  approach (e.g. Hi Tacan or Low Tacan)?
What are the differences between these two approaches?

I was told, last century, the choice between Hi and Low was dependent on the theater.  That is, the Hi approach was used (or practiced) for areas that may contain hostile aircraft.


text:
What are the limits on myopia for a pre-eye refraction surgery for a class 1 medical certificate?
Are there any limitations for myopia (-number) for a pre-eye refraction surgery for a class 1 medical certificate? I live in India & I have -6.5 & -7.5 in the left & right eye respectively.

It looks like there are no limits for your pre-surgery eyesight:

Flight crew having undergone refractive surgery will be considered for
  medical fitness for flying on a case-to-case basis. Such cases will be
  examined only after a minimum period of six months after the
  procedure. Medical fitness for initial issue of licence may also be
  considered for such cases, if the visual requirements for the license
  category are met with normal corneal topography, no post surgical
  complications like corneal opacity interfering with vision and
  unstable refraction.

That makes sense: LASIK physically changes your eyes, so whatever your values were before the surgery are completely irrelevant after it. The general class I eyesight requirements in India are taken from ICAO Annex 1, which isn't freely available online. However, ICAO's Manual of Civil Aviation Medicine says:

Distant visual acuity with or without correction shall be 6/9 or
  better in each eye separately, and binocular visual acuity shall be
  6/6 or better. No limits apply to uncorrected visual acuity.


text:
Is there any benefit to science from the Swiss built solar plane flying across the globe?
Are there any innovations that were made during the development or flight of the Solar Impulse plane that would go into any type of regularly used airplanes in the near future?

are you asking if Is there any benefit to science or any innovations that would go into any type of regularly used airplanes in the near future? those are quite different questions, and the first is heavily faulted.

I can see the idea behind the question but it's very speculative. The pioneers in many different fields had no idea how or if their work would be used in the future, and predictions were often wrong.

Hate to say it, but this question calls for some very speculative answers and, as a result, the answers are going to be opinion based.  This would be better for a discussion based forum (like reddit.com/r/aviation).  Or perhaps in chat here.

As you can see from the massive delay in its flight schedule, the Solar Impulse II has run into some problems. This is always an indication that something has been learned. Unfortunately, what has been learned is that electric flight is even harder than expected.
The value of this particular airplane is the demonstration that purely electric long-range flights are possible, and in this it ranks with the first rocket-powered airplanes in 1928 and 1929 - yes, it can be done, but for now there is no practical value in it.
As for long term developments - this is just speculation, but I doubt that in 50 or 100 years we will see the Solar Impulse II as the starting point of a new era.